In some vapour compression systems an ejector is arranged in a refrigerant path, at a position downstream relative to a heat rejecting heat exchanger. Thereby refrigerant leaving the heat rejecting heat exchanger is supplied to a primary inlet of the ejector. Refrigerant leaving an evaporator of the vapour compression system is supplied to a secondary inlet of the ejector.
An ejector is a type of pump which uses the Venturi effect to increase the pressure energy of a fluid at a suction inlet (or secondary inlet) of the ejector by means of a motive fluid supplied to a motive inlet (or primary inlet) of the ejector. Thereby, arranging an ejector in the refrigerant path as described will cause the refrigerant to perform work, and thereby the power consumption of the vapour compression system is reduced as compared to the situation where no ejector is provided. It is desirable to allow as large a portion as possible of the refrigerant leaving the evaporator to be supplied to the secondary inlet of the ejector.
An outlet of the ejector is normally connected to a receiver, in which liquid refrigerant is separated from gaseous refrigerant. The liquid part of the refrigerant is supplied to the evaporator, via an expansion device. The gaseous part of the refrigerant may be supplied to a compressor. Thereby the gaseous part of the refrigerant is not subjected to the pressure drop introduced by the expansion device, and the work required in order to compress the refrigerant can therefore be reduced.
When the ambient temperature is high, such as during the summer period, the temperature as well as the pressure of the refrigerant leaving the heat rejecting heat exchanger is relatively high. In this case the ejector performs well, and it is advantageous to supply all of the refrigerant leaving the evaporator to the secondary inlet of the ejector, and to supply gaseous refrigerant to the compressors from the receiver only. When the vapour compression system is operated in this manner, it is sometimes referred to as ‘summer mode’.
On the other hand, when the ambient temperature is low, such as during the winter period, the temperature as well as the pressure of the refrigerant leaving the heat rejecting heat exchanger is relatively low. In this case the ejector is not performing well, and it is advantageous to supply the refrigerant leaving the evaporator to the compressors, instead of to the secondary inlet of the ejector. When the vapour compression system is operated in this manner, it is sometimes referred to as ‘winter mode’.
When the ambient temperature decreases in such a manner that a switch from a ‘summer mode’ operation of the vapour compression system to a ‘winter mode’ operation of the vapour compression system is required, such a switch can be ensured relatively easy on the basis of the pressure inside the receiver. However, when the ambient temperature increases in such a manner that a switch from a ‘winter mode’ operation of the vapour compression system to a ‘summer mode’ operation of the vapour compression system is required, or more beneficial, such a switch may not occur automatically during operation of the vapour compression system. It may therefore be desirable to take measures to ensure that a switch to the ‘summer mode’ is in fact performed in this situation.
US 2012/0167601 A1 discloses an ejector cycle. A heat rejecting heat exchanger is coupled to a compressor to receive compressed refrigerant. An ejector has a primary inlet coupled to the heat rejecting heat exchanger, a secondary inlet and an outlet. A separator has an inlet coupled to the outlet of the ejector, a gas outlet and a liquid outlet. The system can be switched between first and second modes. In the first mode refrigerant leaving the heat absorbing heat exchanger is supplied to the secondary inlet of the ejector. In the second mode refrigerant leaving the heat absorbing heat exchanger is supplied to the compressor.